I've looked into the code and it seems like it's these two things that are causing it:
.jsenabled.docked-region-side-pre.empty-region-side-pre.used-region-side-post #region-main {
width: 100%;
}
.empty-region-side-pre.used-region-side-post #region-main {
width: 100%;
}
Where do I go to get rid of these 2 lines?
Thanks.